1. Field of the Invention
This invention relates to hydraulic fluids for the protection of equipment, such as downhole tools used in oil and gas exploration and production. More particularly, this invention relates to hydraulic fluids that can protect tools from adverse effects resulting from water leakage into the tools.
2. Background Art
Hydraulic fluids are used in various tools, including downhole tools used in oil and gas exploration and production. Hydraulic fluids in these tools serve diverse functions including lubrication, force transduction, pressure compensation, and insulation for various electronic components in the tools. For example, electronic components that are critical for safe and functional operations of a tool may be protected in a chamber filled with a dielectric hydraulic oil.
While embodiments of the invention may be applied to various kinds of tools or equipment, the following description uses a downhole tool for illustration. One of ordinary skill in the art would appreciate that the use of a downhole tool is for clarity of illustration and is not intended to so limit the scope of the invention.
FIG. 1 shows a downhole tool 101 disposed in a borehole 102. The downhole tool 101 can be any tool that is used in the drilling, logging, completion, or production of the well, including for example a bottom-hole assembly (which may include various measurement-while-drilling (MWD) or logging-while-drilling (LWD) sensors), formation fluid tester (e.g., the MDT™ tool from Schlumberger Technology Corp, Houston, Tex.), etc. The downhole tool 101 is deployed on a wireline, drill string, TLC or coiled tubing 103.
FIG. 2 shows a section of downhole tool 101 in a working environment. The downhole tool 101 may include, among other things, electronic components 201 protected in an oil-filled chamber 202. The oil-filled chamber 202 is filled with a suitable hydraulic oil 203, such as Exxon Univis J-26™. One of ordinary skill in the art would appreciate that the types of oils used are not germane to the present invention and should not limit the scope of the invention. The oil-filled chamber 202 is typically separated from the outside environment by a seal 204, which may be an o-ring, gasket, valve seat, or the like.
Downhole tools may be exposed to high temperatures (up to 250° C.) and high pressures (up to 20,000 psi) in the downhole environment. The high pressures downhole may create a significant pressure overbalance relative to hydraulic pressures inside the downhole tools. Such pressure overbalance may lead to leakage of wellbore fluids into the tool hydraulic sections. In addition, the high temperatures in the downhole environment may cause the seal to fail. Either of these conditions may result in leakage 205 of borehole fluid into the oil-filled chamber 202. The borehole fluid may include significant amounts of water. The water leaked into the oil-filled chamber may become droplets entrained 206 in the oil 203. The entrained water will eventually settle to the lowest part of the oil-filled chamber 202, shown as water 207. The entrained water 206 or the settled water 207 may provide conductive paths which cause a short in the electronic components 201.
In addition to causing shorts in electronic components, the water trapped in oil chambers may also degrade components that are not designed to be exposed to water, particularly at the high temperatures and high pressures found downhole. For example, polyimides are often used as insulating materials for electronic components in a downhole tool. Polyimides may be hydrolyzed by water under high temperature and high pressure conditions. Similarly, long term exposure to the trapped water may lead to corrosion of metal parts. Any of these adverse effects will eventually result in tool failure or malfunction, which is costly and may present a safety hazard.
An approach to prevent damage from water collected at the bottom of the oil-filled chamber is to add a higher density dielectric fluid, such as FC-70 (Fluorinert™ from 3M Specialty Materials of St. Paul, Minn.), to the hydraulic oil. However, such additives (e.g., Fluorinert™) are often found to negatively affect the performance of the hydraulic fluids in the tool. Also, this approach is dependent on tool orientations, and may not work in deviated well conditions.
Other approaches to avoid the adverse effects of water leakage into a tool include identification of potential leakage locations and then engineering the tool to minimize the risk of leaks occurring at these locations. However, this approach is not always foolproof.
Therefore, there exists a need for further methods to reduce or eliminate the adverse effects of water leakages into the oil-filled chambers in the downhole tools.